This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-288499, filed Sep. 21, 2001; and No. 2002-272845, filed Sep. 19, 2002, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus, image processing apparatus, motion information image generating method which provide effective information for medical diagnoses.
2. Description of the Related Art
It is very important for the diagnosis of living tissue such as the myocardium to objectively and quantitatively evaluate the function of the tissue. For example, conventional quantitative evaluation methods mainly associated with the heart will be described below.
A method using the myocardial velocity gradients (MVG) defined by two-dimensional images is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-155862. The MVGs defined by two-dimensional images include an MVG-S for a short-axis plane and an MVG-L for a long-axis plane (four- or two-chamber plane based on an apical long-axis). According to currently practical MVG-S/L, a region of the myocardium and its local motion direction can be determined by manually setting the contours of the endocardium and epicardium coats of the myocardium in a two-dimensional image at a given time phase, and a myocardial velocity gradient, i.e., a strain rate, is obtained in each range of the myocardium.
Jpn. Pat. Appln. KOKAI Publication No. 9-201361 discloses an MVG-M method in which when the positions of two points (preferably on the endocardium and epicardium coats) of the myocardium are given at an initial time phase, the positions of two points (on the endocardium and epicardium coats) are automatically tracked at other time phases by using the TDT (Tissue Doppler Tracking) method, thereby obtaining MVGs at all the time phases. A technique of obtaining a strain as a value representing tissue deformation and displaying it in real time is also disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-70303.
The significance of obtaining motion parameters in a local range inside the myocardium is described in reference 1 (xe2x80x9cDifference between Endocardial Myocardium and Epicardial Myocardium of Left Ventricular Wallxe2x80x9d, J Cardiol 2000; 35: 205-218). According to this reference, in the case of the healthy myocardium, the endocardium coat side contributes to contraction more dominantly (about twice) than the epicardium coat side, whereas in a case of ailment, e.g., cardiac infarction, this contribution of the endocardium coat side reduces. Although this fact has been known from animal experiments, recent studies using the MVG-M to be described later and the like have revealed that the same applies to humans. The noninvasive, quantitative evaluation of local functions inside the myocardium as well as the function of the overall myocardium is expected to be useful for the comprehension of the progress of a disease and the selection of a medical treatment for the disease, and hence has gained in importance.
In the conventional MVG method, however, in order to analyze a plurality of time phases of the cardiac time phases, a myocardial region must be set in each of the time phases, resulting in difficulty in analyzing changes in MVG-S/L over time. In addition, since MVG-S/L is used to obtain a motion parameter based on the size of the myocardium, such as the demarcation size of the myocardium, it is difficult to obtain distribution information in a local range inside the myocardium.
In the conventional MVG-M method, since the velocity gradient of an M-mode image is displayed, temporal analysis can be performed relatively easily. However, in the MVG-M method, since only one-dimensional information is provided, two-dimensional distribution information cannot be obtained.
In addition, a characteristic common to computations of strain rates such as velocity gradients is that spatial differentiation is performed by using velocity information that tends to be spatially unstable due to the influence of speckle noise and the like unique to ultrasounds. For this reason, it is difficult to perform stable computations concerning a living body due to noise.
In the conventional strain display method, the strain rate between two points of a region having a fixed length temporally is obtained on the assumptions that the region has spatially uniform strain, and the strain is included in a predetermined interval. These assumptions do not hold in the case of evaluation of the heart, especially a short-axis plane. Therefore, accurate strain cannot be obtained.
The present invention has been made in consideration of the above situation, and has as its object to provide an ultrasound image apparatus, and motion information image generating method which provide a motion information image representing displacement or strain with high stability even if the image is generated from a living tissue such as the heart.
In order to achieve the above object, the present invention has the following means.
The present invention may provide an ultrasonic diagnostic apparatus which comprises: a memory which stores a plurality of ultrasonic images which corresponds to a plurality of time phases and are concerning with an object; a distribution image generation unit configured to generate a plurality of distribution images of motion velocities in the plurality of the time phases on the basis of the plurality of the ultrasonic images; a tracking point setting unit configured to set tracking points in a tissue range of the object in an image which is one of the plurality of ultrasonic images and corresponds to a predetermined time phase; an estimation unit configured to estimate corresponding points which correspond to the tracking points in the plurality of ultrasound images corresponding to remaining time phases other than the predetermined time phase, on the basis of the plurality of distribution images of motion velocities; a signal value determining unit configured to determine signal values at the tracking points and the corresponding points in each of the plurality of the time phases according to stretch of the tissue range of the object; a motion information image generating unit configured to generate a motion information image on the basis of the signal values at the tracking points and the corresponding points; and a display unit configured to display the motion information image.
The present invention may provide an ultrasonic diagnostic apparatus which comprises: a memory which stores a plurality of ultrasonic images which corresponds to a plurality of time phases and are concerning with an object; a center point of contraction setting unit configured to set a first center point of contraction in a tissue range of the object and a second center point of contraction adjacent to the first center point of contraction; a distribution image generation unit configured to generate a first distribution images of motion velocities in a direction toward the first center point of contraction and a second distribution images of motion velocities in a direction toward the second center point of contraction on the basis of the plurality of the ultrasonic images; a tracking point setting unit configured to set tracking points in a tissue range of the object in an image which is one of the plurality of ultrasonic images and corresponds to a predetermined time phase; an estimation unit configured to estimate first corresponding points which correspond to the tracking points on the basis of the first distribution images of motion velocities and second corresponding points which correspond to the tracking points on the basis of the second distribution images of motion velocities, in the plurality of ultrasound images corresponding to remaining time phases other than the predetermined time phase; a signal value determining unit configured to determine signal values at the tracking points associated with a stretch of the tissue range in each of the time phases and signal values at the first corresponding points and the second corresponding points in the remaining time phases other than the predetermined time phase; a motion information image generating unit configured to generate a first motion information image on the basis of the signal values at the tracking points and the first corresponding points and a second motion information image on the basis of the signal values at the tracking points and the second corresponding points; a compound image generating unit configured to generate a compound image compounded the first motion information image and the second motion information image; and a display unit configured to display the compound image.
The present invention may provide a motion information image generating method which comprises: generating a plurality of distribution images of motion velocities in a plurality of time phases on the basis of a plurality of a ultrasonic images which corresponds to a plurality of time phases and are concerning with an object; setting tracking points in a tissue range of the object in an image which is one of the plurality of ultrasonic images and corresponds to a predetermined time phase; estimating corresponding points which correspond to the tracking points in the plurality of ultrasound images corresponding to remaining time phases other than the predetermined time phase, on the basis of the plurality of distribution images of motion velocities; determining signal values at the tracking points and the corresponding points in each of the plurality of the time phases according to stretch of the tissue range of the object; generating a motion information image on the basis of the signal values at the tracking points and the corresponding points; and displaying the motion information image.